The OSBP was a project in which all 20 participants wore red "No" or green "Yes" badges to signal their interest in participating. Participants could approach those who were wearing "Yes" buttons (approximately equally distributed between men and women) and asked if they could touch their breasts or butt. The person asked would then give or refuse their consent. The rules of the project forbade asking this of those wearing "No" buttons or those not wearing buttons. People became participants by noticing the buttons and asking about it.
OSBP was not in any way sponsored by Penguicon. Only about two dozen people wore the buttons, most of whom were a close group of friends who organized OSBP, and the Penguicon organisers (and most attendees) were unaware of the OSBP project at the time it occurred.
A fairly thorough timeline of posts about it, with quotes, as been collected in this feminist sf wiki article.
- Women's bodies: just like open source software! (Feministing)